26.10 The Human Eye - PowerPoint PPT Presentation

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26.10 The Human Eye

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The eyeball is approximately spherical with a diameter of about 25 mm. Light enters the eye through a transparent membrane (the cornea ). This membrane covers a clear liquid region (the aqueous humor ), behind which is a diaphragm (the iris ), the lens, a region filled with a jelly-like substance (the vitreous humor ), and, finally, the retina. The retina is the light-sensitive part of the eye, consisting of millions of structures called rods and cones. When stimulated by light, these structures send electrical impulses via the optic nerve to the brain, which interprets the image on the retina.

(a) When fully relaxed, the lens of the eye has its longest focal length, and an image of a very distant object is formed on the retina. (b) When the ciliary muscle is tensed, the lens has a shorter focal length.

A farsighted person has a near point located 210 cm from the eyes. Obtain the focal length and power of the converging lenses in a pair of contacts that can be used to read a book held 25.0 cm from the eyes.